1. Field of the Invention
This invention relates to a liquid crystal display module, and more particularly to an optical sheet and a method of assembling a liquid crystal display module that is capable of preventing an inflow of impurities on a backlight unit, thereby minimizing screen staining caused by the impurities.
2. Description of the Background Art
Generally, a notebook personal computer NTPC is manufactured in a notebook size to enable a user to access information during the course of the movement. A liquid crystal module LCM is used as a display device for displaying information in the NTPC.
The LCM includes a liquid crystal display panel and a driving circuit part for driving the liquid crystal display panel. The liquid crystal display panel includes liquid crystal cells arranged in matrix form between two glass substrates and switching devices for switching a signal supplied to these liquid crystal cells. Because the LCM includes glass substrates which can be easily damaged by an external impact, a case is used to protect the outer part of the LCD in order to prevent such damage.
Referring to FIG. 1, a conventional LCM includes a support main 14, a liquid crystal display panel 2 deposited on the support main 14, a top case 10 covering the edge of the liquid crystal display panel 2 and the support main 14, and a backlight unit having a plurality of optical sheets 32, 34, 36 and a light guide panel 24.
In the liquid crystal display panel 2, a liquid crystal is interposed between two glass substrates to which an upper and a lower polarizing plate 42, 40 are adhered respectively, and a thin film transistor TFT drives each of liquid crystal cells (arranged in matrix form).
The top case 10 is bent at a right angle to cover the side surface of the support main 14 and the edge of the liquid crystal display panel 2. The support main 14 and the top case 10 are assembled with screws (not shown).
The support main 14 is generally made as a molding, but has recently been manufactured of a metal such as aluminum Al, which has excellent heatproof against high temperature, in correspondence to a high brightness television or a high brightness monitor. A reflecting plate 26 is located at the bottom of the support main 14, and the light guide panel 24 and the optical sheets 32, 34, 36 are deposited on top of it. The liquid crystal display panel 2 is mounted on the optical sheets 32, 34, 36 in the support main 14.
The backlight unit includes a lamp 20 for generating light, a lamp housing 16 shaped to adequately cover the lamp 20, a light guide panel 24 for converting the incident light from the lamp 20 to the planar light source, a reflecting plate 26 installed at the rear of the light guide plate 24, and optical sheets on which a diffusion sheet 32, a lower prism sheet 34 and an upper prism sheet 36 are sequentially deposited.
A cold cathode fluorescent lamp CCFL is mainly used as the lamp 20, and the light generated at the lamp 20 is incident to the light guide panel 24 through an incident surface located at the side surface of the light guide panel 24.
The lamp housing 16 has a reflecting surface on the inside of it to reflect the light from the lamp 20 to the incident surface of the light guide panel 24. The light guide panel 24 is manufactured in the shape of its rear surface (being inclined) and its front surface (being flat). The reflecting plate 26 reflects the light incident to itself from the rear surface of the light guide panel 24 to the light guide panel 24, thereby reducing the loss of light. That is, if the light from the lamp 20 is incident to the light guide panel 24, it is reflected in a tilt angle at the rear surface (being the inclined surface) to progress toward the front surface uniformly. At this moment, the light progressed to the lower surface and the side surface of the light guide panel 24 is reflected at the reflecting plate 26 to progress toward the front surface. The light passing through the light guide panel 24 is diffused to an entire area by the diffusion sheet 32.
On the other hand, the light incident to the liquid crystal display panel 2 has higher light efficiency when it is incident perpendicularly. For this cause, it is desirable to deposit two forward direction prism sheets to cause the progression angle of the light coming out of the light guide panel 24 to be perpendicular to the liquid crystal display panel. The light passing through the diffusion sheet 32 is incident to the liquid crystal display panel 2 via the lower and the upper prism sheets 34, 36.
In a method of assembling such a LCM, the reflecting plate 26 is mounted on the bottom surface of the support main 14, the light guide panel 24 is then mounted on the reflecting plate 26, the backlight unit including the diffusion sheet 32, the lower prism sheet 34 and the upper prism sheet 36 are then mounted on the light guide panel 24, and the liquid crystal display panel 2 is then mounted on the backlight unit.
In the backlight assembling process of such an LCM, an upper and a lower peeling sheet 44, 46 (as shown in FIG. 2) are attached to the upper prism sheet 36 for protecting the upper prism sheet 36 itself and preventing the inflow of impurities from the outside before the upper prism sheet 36 is mounted.
Polyethylene, (a semitransparent material) is used for the upper and the lower peeling sheet 44, 46. In the event that the upper prism sheet 36 (to which the upper and the lower peeling sheet 44, 46 are adhered) is mounted on the lower prism sheet 34, firstly the lower peeling sheet 46 and the upper peeling sheet 44 are peeled away from the upper prism sheet 36, and then the upper prism sheet 36 is mounted on the lower prism sheet 34. A reason why the upper and the lower peeling sheet 44, 46 are removed from the upper prism sheet 36 is because the upper and the lower peeling sheet 44, 46 is of the semitransparent material. As a consequence, the screen inspection of the backlight unit (described later) cannot be carried out.
After the upper prism sheet 36 has been mounted on the lower prism sheet 34, the screen inspection of the backlight unit is carried out. The screen inspection of the backlight unit is performed because of possible inflow of impurities (causing stains), or other damage such as scratches. The backlight unit is inspected in-use, with light passing through the light guide panel 24, the diffusion sheet 32, the lower prism sheet 34 and the upper prism sheet 36 by driving the lamp 20.
After the completion of the screen inspection of the backlight unit, the LCM whereon the backlight unit is mounted, is packed to be transferred to a liquid crystal display panel assembling process. In the liquid crystal display panel assembling process, the liquid crystal display panel 2 is mounted to correspond to the top of the light guide panel 24, the diffusion sheet 32, the lower prism sheet 34 and the upper prism sheet 36 on the support main 14.
In this manner, when assembling the conventional LCM, because the upper and the lower peeling sheet 44, 46 are removed from the upper prism sheet 36 for the screen inspection of the backlight unit mounted on the support main 14, the surface of the backlight unit is exposed to the outside during the job waiting time between the assembling processes of the liquid crystal display panel 2. Due to the external exposure of the surface of the backlight unit, impurities flow in from the outside onto the surface of the backlight unit. Due to such impurities flowing into the backlight, screen staining such as white spots and black spots occur upon driving of the conventional LCM.